A standard cold-rolling stand has a support frame, a pair of small-diameter working rolls rotatable about respective horizontal, parallel, and vertically spaced axes defining a workpiece nip, and a pair of large-diameter backup rolls rotatable about respective axes parallel to and vertically flanking the working-roll axes and defining a vertical plane offset from the plane of the working-roll axes. Each backup roll bears vertically on the respective working roll and the rolls of each pair are counterrotated to draw an elongated workpiece of predetermined maximum width generally perpendicular to the planes through the nip. The rolls are pressed vertically toward the nip to compress and deform the workpiece in the nip.
In order to maximize pressure on the workpiece, the diameter of the working rolls is as small as possible, thereby reducing the contact area and increasing the pressure. Since the working-roll plane is offset in the workpiece travel direction from the backup-roll plane, the compressive forces effective parallel to the planes have a component perpendicular thereto which can bow the slender working rolls.
Thus bracing systems are provided in counteract this bowing. The standard practice is to flank each working roll with a pair of small bracing rolls that stiffen the working roll, preventing the stand from vibrating. Such an arrangement is fairly effective but substantially increases the wear of the working rolls while flaws in the strip being rolled can damage the equipment.
Another disadvantage of the known roll stands, as described in German patent documents Nos. 1,777,054, 2,522,213, and 3,212,070 respectively filed June 28, 1966, May 17, 1975, and Apr.01, 1982 by K. Liefeld, H. Rommen et al, and T. Iwanami et al, is that the working rolls are effectively covered up by the bracing equipment, so spraying a coolant and lubricant on them is nearly impossible.
It has been suggested to eliminate this bracing, and to replace it with a lateral offset of the working rolls to compensate for the horizontal forces. Such an arrangement cannot respond rapidly to changing working conditions. Thus for example on closing of the nip at first there is only the rolling force to deal with, the torque and the angular force only becoming effective on startup, that is when the workpiece is fed in. When the strip breaks or has serious flaws, it is impossible to take any effective measures so that the rolls can be damaged.